University of Alaska Fairbanks scientists have identified what they think is the ancestral trait that allowed for the evolution of air breathing in vertebrates. They will present their research at the 42nd annual meeting of the Society for Neuroscience Oct. 17 in New Orleans.
“To breathe air with a lung you need more than a lung, you need neural circuitry that is sensitive to carbon dioxide,” said Michael Harris, a UAF neuroscientist and lead researcher on a project investigating the mechanisms that generate and control breathing. “It’s the neural circuitry that allows air-breathing organisms to take in oxygen, which cells need to convert food into energy, and expel the waste carbon dioxide resulting from that process,” he said. “I’m interested in where that carbon-dioxide-sensitive neural circuit, called a rhythm generator, came from.”
Lampreys are ancient fish that have characteristics similar to the first vertebrates. They do not have lungs and do not breathe air. As larvae, they live in tubes dug into soft mud and breathe and feed by pumping water through their bodies. When mud or debris clogs a lamprey’s tube, they use a cough-like behavior to expel water and clear the tube. A rhythm generator in their brain controls that behavior. Air breathing evolved in fish and allowed the movement of vertebrates to land and the evolution of reptiles, birds and mammals. Without a carbon-dioxide-sensitive rhythm generator, the structure that would become the lung might not have worked as a lung. “The evolution of lung breathing may be a repurposing of carbon dioxide sensitive cough that already existed in lungless vertebrates, like the lamprey,” said Harris.